A configuration in which a belt winding device is provided on a side panel disposed on the front part of a cargo bed behind the pair of left and right occupant seats in a vehicle is known. However, there are cases in which the side panel is not positioned behind the occupant seats, and in such cases it may be difficult to install the seat belt device. In addition, with the configuration disclosed in the known arrangements, it may be necessary to operate the belt so as to fasten the belt around an occupant seated in an occupant seat after the belt has been pulled out upward from an outlet provided on the upper part of the side panel at a position lower than the upper end of the backrest part of the occupant seat. This arrangement may not operate well and may not have a good feel in use, since the belt may be directly fastened so that a load acts on the shoulder area of the occupant from above.